1. Field of the Invention
The present invention relates to energy generation and, more particularly, to energy generation through the plasma treatment of waste materials.
2. Description of Related Art
In 1800, the world population totaled less than 1 billion. In the mere two hundred years between 1800 and 2000, the world population exploded by six times to a total of 6.1 billion inhabitants. Predictions estimate that this number could rise to near 9 billion in the next fifty years. As the population grows exponentially, two corollaries grow along with it: (1) the demand for energy, and (2) the creation of waste. The processes used to create the energy necessary to meet the ever increasing energy demands of the world population and the overwhelming creation of large amounts of waste by the world population are perhaps the two most significant factors contributing to the destruction of the environment.
In the U.S., the fulfillment of the demand for energy is met almost entirely by fossil fuel power plants. Fossil fuel power plants are energy conversion centers that combust fossil fuels to produce electricity. A fossil fuel power plant converts the chemical energy stored in fossil fuels such as coal, fuel oil, or natural gas into thermal energy, then mechanical energy, and finally electrical energy for distribution and use. Significantly, almost 80% of electricity produced in the U.S. comes from power plants that burn coal. A heavy reliance upon fossil fuels for energy generation has many drawbacks. First, the combustion of fossil fuels can create harmful solid and gaseous emissions that must be filtered and controlled to prevent pollution. Second, the solid emissions, such as fly ash, that are filtered from the output of the fossil fuel combustion processes must be deposited into waste facilities, such as landfills. Third, supplies of fossil fuels, such as coal, are finite and will eventually be depleted. In light of the many drawbacks of fossil fuel based energy generation, much emphasis has been placed on finding alternative methods of energy generation.
A large amount of research and development has been conducted into alternative energy sources involving the harvesting of energy from naturally occurring sources. For example, much research has been conducted concerning harvesting geothermal energy, solar energy, and wind energy. As these energy sources are naturally occurring, the by-products associated with their conversion are more limited. These naturally occurring energy sources, however, are somewhat limited in their potential total capacity, especially in view of the rapidly increasing demand for energy.
An additional area of research and development with respect to alternative energy sources, has been focused on harvesting the energy of waste. Energy From Waste (EFW) technologies have been, and continue to be, developed that generate energy as a by-product to the destruction of waste. The most widely known type of EFW facility is incineration. While widely used, incineration facilities are costly, ineffective, and sources of pollution. Most incineration facilities require extensive air pollution control systems to reduce emissions from the waste combustion process below regulatory levels. Additionally, like fossil fuel power plants, incineration facilities generate a significant amount of solid emission by-product in the form of fly ash. This fly ash must be deposited and thus further contributes to landfill expansion.
A significant advancement in pursuit of EFW technologies has been achieved in the field of plasma processing. Plasma processing, or gasification, of waste materials involves the exposure of waste materials to extraordinarily high temperatures that disassociate the organic components into their elemental components and vitrify the inorganic components into a glassy rock-like residue. The energy release from this process can be used to sustain the plasma process and to create electrical energy for distribution. Thus, not only does plasma waste processing present a potential solution that could efficiently and safely dispose of waste materials, but it also represents a potentially viable alternative energy source.
Plasma waste processing facilities are complex systems that differ significantly from combustion type processing facilities. Plasma can generally be described as an electrically conducting gas. Lightning is the most common example in nature. At normal temperatures and pressures, gases are usually very good electrical insulators. This is because the electrons in the gas are tightly bound inside gas atoms and are not free to move in response to externally applied electric or magnetic fields. Under certain conditions, however, some or all of the electrons can be removed from their parent atoms, a process called ionization. The gas then has of a mixture of negatively charged electrons, positively charged atoms, called ions, and un-ionized neutrally charged atoms. Now the electrons and ions are free to move under the action of applied electromagnetic fields and the gas can conduct electricity. Due to their much smaller mass the electrons respond to the applied fields much more readily than the ions and, consequently, carry most of the current. Since electrons and ions are produced in pairs and have opposite charges most of the plasma remains electrically neutral.
Because the plasma is a gas and cannot melt, it can be used in a “plasma torch” as a resistive heating element capable of producing temperatures exceeding 7000 degrees Celsius, up to three times hotter than those produced by combustion and hotter than the surface of the sun.
As described in U.S. Pat. No. 5,280,757, U.S. Pat. No. 5,143,000, U.S. Pat. No. 3,779,182, and other prior art, plasma arc heated processes have received considerable attention for waste treatment over fuel combustion heated processes because of several distinct advantages of plasma heat which is well suited for the pyrolysis and vitrification of waste materials. A plasma arc torch operates by supporting a high voltage electric arc on a flow of plasma (ionized) gas to generate an extremely hot “flame.” The quantity of plasma gas flowing through the plasma torch is significantly less than the quantity of gas required to release the equivalent heat energy by the combustion of hydrocarbon fuels. A further difference and advantage of a plasma torch heat source over a combustion heat source is that the plasma torch can be used to produce useful by-product gases of higher caloric content referred to as the degassing process. In addition, by virtue of the fact that a plasma arc torch uses only a small quantity of gas to support the arc and generate the heat, combustion is unlikely to occur spontaneously in the materials which are being heated. A major advantage of the plasma torch is that it is capable of unusually high rates of heat transfer, adding to its inherent efficiency. Also, the temperature of 4,000-7,000 degrees Celsius generated by a plasma torch is much hotter than that generated by a combustion source and is hot enough to melt known materials simultaneously with the pyrolysis degassing process.
Conventional systems have been relatively successful in demonstrating the theoretical possibility of recovering the energy of Municipal Solid Waste (“MSW”) with plasma processing. For example, some prior art systems have shown that it may be possible to recover over 90% of the energy value of a waste stream.
Despite the overwhelmingly exciting theoretical benefits, the implementation of plasma waste processing facilities and systems in practical environments have been extremely limited due to implementation obstacles and to the deficiencies of the prior art systems. The difficultly in achieving efficient and cost effective implementations of plasma waste processing facilities is perhaps best illustrated by the fact that despite their tremendous possible benefits, there are only two known commercial plasma waste processing facilities in the world, all located in Japan. The implementation of plasma waste processing facilities has been significantly hindered by many factors. One primary hindrance is due to the relatively large capital cost associated with the initial provisioning of a plasma waste processing facility. The construction and provisioning of the multiple complex elements of a plasma waste processing facility, including the plasma reactor, gas treatment systems, and the electrical generator systems, require a significant amount of initial investment. Additionally, the efficiency of plasma waste processing facilities are closely tied to economies of scale. For example, a smaller facility with a relatively small daily volume of MSW will inherently be less efficient than a larger facility with a relatively large daily volume of MSW. Furthermore, some plasma reactor configurations are less well suited for energy recovery due to the relatively high plasma energy requirements (500 to 600 kWhr/ton of waste) of certain types of arc plasma torches.
Accordingly, there is a need in the art for a more efficient method by which to recover energy from waste.
Additionally, there is a need in the art for an efficient method to integrate a plasma waste processing system into an existing energy generation system.
Additionally, there is a need for the ability to use plasma waste processing systems with high efficiency generators.
Additionally, there is a need in the art for plasma waste processing system that can reliably covert a high percentage of energy of a waste stream.
Additionally, there is a need in the art for a plasma waste processing system that can generate energy in an efficient manner.
Additionally, there is a need in the art for a plasma waste processing system that can improve the efficiency, cost effectiveness, and environmental performance of existing energy generation systems.